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May 14, 2009 -- A water-soluble extract of the plant kava was found to be safe and highly effective for the short-term treatment of anxiety in a new study. But concerns about its long-term safety and the safety of other kava formulations remain.

A decade ago, kava supplements were a popular alternative treatment for anxiety and related conditions, with U.S. sales approaching $50 million in 1998 alone.

But reports of liver damage and even liver failure linked to its use led to bans of kava supplements in many countries, including Canada, Germany, France, and the U.K.

Kava was not banned in the U.S., but sales fell dramatically after the FDA issued a warning about possible liver-related injury in March 2002.

Kava Under Scrutiny

In 2007, a safety panel of the World Health Organization (WHO) reported a possible link between kava use and seven deaths and 14 liver transplants, mostly in Europe.

But the WHO report suggested that liver toxicity may be limited to kava formulations that used the whole kava plant, instead of just the root, or used acetone and ethanol to extract the active ingredient from the plant instead of water.

"Kava has been used in the Pacific Islands where it is grown for centuries without evidence of liver problems," researcher Jerome Sarris, of Australia's University of Queensland tells WebMD. "But they only use water-soluble extract and they only use the peeled root of the plant."

Sarris says he used a product that mirrored the traditional kava used by the Pacific Islanders as closely as possible in his study, published in Psychopharmacology.

Thirty-seven people with generalized anxiety and varying levels of the depression completed the three-week long trial. In the first week, all participants took a placebo. In the second week, half the participants took kava tablets and the other half took placebo tablets. In the third week, the group that had taken kava tablets was switched to a placebo and the group that had taken a placebo switched to kava tablets. Participants were not aware whether they were taking a placebo or kava tablets.

As measured by standardized anxiety and depression questionnaires, the participants reported much less anxiety when they were taking the kava than when they took placebo pills, Sarris says.

Depression levels also dropped among many patients who reported depression and no serious side effects were associated with kava use.

Because the patients took the kava for only one week, the study did not address the long-term safety of the water-extracted, kava root formulation.

Sarris hopes to conduct a longer study comparing kava to drugs that are widely prescribed for the treatment of anxiety.

"What we can say is the evidence supports the use of this [formulation] for short periods for acute anxiety and stress," Sarris says.

Let the Buyer Beware

But East Carolina University professor of psychiatric medicine Richard Bloch, PhD, tells WebMD that the lack of regulation of dietary supplements like kava in the U.S., means consumers can never be sure what they are getting.

"The FDA doesn't monitor the ingredients used, how these products are prepared, or even if the doses are accurate," he says. "Manufacturers can say whatever they like and you don't know for sure if it is accurate because nobody is really checking."

Bloch recently reviewed the research examining the safety of kava for the treatment of anxiety. He says not enough high-quality, long-term studies have been done to truly understand the effect that kava has on the liver.

"This study suggests that kava is very effective for treating generalized anxiety disorder, but it was just a three-week trial," he says. "It does not address the long-term safety of kava or its long-term efficacy. We simply do not know if this treatment would be safe and effective if used for six months or a year."